2. Presented by: Muhammad Usman Mughal
Roll Number: 25
Class: Msc Botany 3rd Semester
Session: 2013-2015

3. 1. Introduction
2. What is calvin cycle?
3. What is regulation of calvin cycle?
4. Rubisco enzyme activation system
5. Ferredoxin-thioredoxin system
6. Ionic movement modulate the enzymes
7. Formation of supramolecular complexes
8. Conclusion
9. References
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5.  Carbon fixation cycle/ Reductive pentose phosphate
cycle/ Calvin Benson cycle/ C3 cycle
 Series of biochemical redox reactions in stroma of
chloroplast
 Independent of light
 CO2 convert into carbohydrates in the presence of
ATP,NADPH
 Opposite to Kreb cycle/ citric acid cycle
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7.  The rate of calvin cycle does not remain constant
 All intermediates present in adequate concentration
in light e.g CO2, ATP, NADPH, ions, Enzymes
 Turned off when not needed in dark
 Mainly regulate by the amount of enzymes in stroma
 Light modulates the expression of stromal enzymes
via specific photoreceptor (phytochrome and blue
light receptor)
 Structure and activity of enzyme modified by two
methods 1) covalent bonds 2) ionic composition
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8.  Calvin cycle itself independent of light but the
enzymes which regulate calvin cycle are dependent on
light
 Light dependent modulation mechanism change the
activity of five key enzymes
1. Rubsico
2. Fructose-1,6-bisphosphatase
3. Sedoheptul0se-1,7-bisphosphatase
4. Phosphoribulokinase
5. NADPH-glyceraldehyde-3-phosphate dehydrogenase
 Generally there are four regulation systems
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9.  Ribulose bisphosphate carboxylase
 Most abundant protein on the earth to date
 Activity of Rubisco increases in the light
 CO2 play dual role in the activity of rubisco
1) activate the enzyme 2) substrate for carboxylation
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10.  Light controls the activity of four remaining enzyme
via ferredoxin-thioredoxin system
1. Fructose-1,6-bisphosphatase
2. Sedoheptul0se-1,7-bisphosphatase
3. Phosphoribulokinase
4. NADPH-glyceraldehyde-3-phosphate
dehydrogenase
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11.  Ferredoxin-thioredoxin system consist of
1. Ferredoxin
2. Ferredoxin-thioredoxin reductase
3. Thioredoxin (regulatory protein)
 Thioredoxin protect against damage caused by
reactive oxygen species (H2O2, O2-,OH-)
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12.  Due to illumination of light H+ moves from stroma to
thylakoid space (pH of stroma increases from 7 to 8)
 In this response of hydrogen ions, Mg2+ moves from
thylakoid space to stroma (formation of E-carbamate
complex)
 Enzymes require Mg2+ are more active at pH 8 than 7
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13.  Enzyme Phosphoribulokinase (PRK) and
glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
bound to CP12 (protein) with the help of disulfide
bonds to hold the complex (supramolecular complex)
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15. Taiz, T. and Zeiger, E. 2006, Plant physiology, 4th
Edition, pp 205 to 208.
https://www.boundless.com/microbiology/textbook
s/boundless-microbiology-textbook/microbial-
metabolism-5/biosynthesis-52/regulation-of-the-
calvin-cycle-339-7097/
http://en.wikipedia.org/wiki/Light-
independent_reactions#Light-dependent_regulation
 http://5e.plantphys.net/article.php?ch=8&id=81
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